Machines such as, for example, wheel tractor scrapers, dozers, motor graders, wheel loaders, and other types of heavy equipment are used to perform a variety of earth-moving tasks. For example, a wheel tractor scraper may be used for excavating, hauling, and dumping an excavated material. A wheel tractor scraper may be used in an operating cycle to cut material from one location during a load phase, transport the cut material to another location during a haul phase, unload the cut material during a dump phase, and return to an excavation site during a return phase to repeat the operating cycle. However, removal of large amounts of material can be difficult for an unskilled or inexperienced operator to achieve efficiently. For example, an unskilled operator may attempt to remove a maximum amount of material during each load phase, but may only be able to do so at a very slow speed. Another unskilled operator may attempt to travel quickly, but may only be able to remove a very small amount of material during each load phase at that speed. Finding the most productive combination of load and travel speed can be complicated, especially when manually performed by an inexperienced operator. Poor productivity and low efficiency can be costly to a machine owner. Because of these factors, the completion of some tasks by a completely operator-controlled machine can be expensive, labor intensive, time consuming, and inefficient.
One method of improving the operation of a machine under such conditions is described in U.S. Pat. No. 6,125,561 (the '561 patent) issued to Shull on Oct. 3, 2000. The '561 patent describes an automatic depth control system of a scraper bowl based on a force error signal between a measured force and a target force. The measured force is derived by a sensor on the scraper bowl. An operator manually inputs the target force value to a computer module depending on a material acting on the scraper bowl. The force signal error, being the difference between the measured force and the target force value, is converted by the computer module to automatically adjust the depth of cut performed by the scraper bowl. Additionally, the scraper bowl can be further controlled by constraining vertical speed to prevent digging too deep or breaking through the ground.
Although the control system of the '561 patent may be capable of improving machine productivity, its use may be limited. Because the automated control of the scraper bowl is based on a predefined target force value associated with the condition of the material acting on the scraper bowl, the cutting depth of the scraper bowl may hinge on the operator's assessment of the material. An operator error may result in inaccurate cutting depth and inefficiency of the task at hand. Also, the machine may encounter terrain of a worksite which varies in condition. An operator may be required to alter the target force value between conditions which may be time consuming, inefficient, and labor intensive. The operator may not be aware of the varying material conditions of the terrain and leave the target force value unchanged. This may result in inaccurate cutting depth of the scraper bowl and an inefficient and unproductive excavation.
The disclosed system is directed to overcoming one or more of the problems set forth above.